Although there are many possible causes of detrimental and pathological changes in the integrity and function of the temporomandibular joint (TMJ), one of the most common is the long term sequelae of internal derangements.
A late stage internal derangement of the TMJ constitutes complete anterior dislocation of the disk, usually of many years duration, along with progressive degenerative changes of the joint, both hard and soft tissues, and even possible collapse of posterior facial height with subsequent facial deformity and major occlusal changes. The principle pathologic finding in such cases is irreversible damage to articular bearing surfaces of the articular eminence and condyle head. The surfaces are usually found to be degenerated, remodeled and with roughened, fibrillated fibrocartilage, and direct bone on bone articular contact. Only remnants of the anteriorly dislocated degenerated articular disk remain. Usually a perforation is present in the disk posterior attachment region, through which the damaged articulating surfaces are in contact. Patients complain of a grating sound symptom in this condition and the corresponding medical physical sign on direct palpation is “crepitus”, which is nearly always present. Joint pain and dysfunction can become unremitting and significant quality of life issues become evident.
Numerous conservative and operative procedures have been used over the years to ameliorate symptoms of TMJ pain and dysfunction. In particular, for advanced conditions as described above there have been attempts to surgically replace damaged bearing surfaces in the TMJ. Nearly all such procedures have necessitated major resection of boney parts of the TMJ with complete or partial removal of the condyle as well as marked resection or removal of the articular eminence.
Such procedures are characterized by the use extra-articular fixation methods (outside of the joint capsule) with multiple screws and bone cement. Most procedures involve long metal shanks covering a good portion of the mandibular ramus with multiple bone screws to fixate the condyle portion of the joint and similar methods with screws and bone cement to fixate the articular eminence and/or upper bearing surface replacement.
It is noteworthy also in such procedures that various masticatory muscles are elevated from their boney surface attachments and specifically the attachment of the lower head of the lateral pterygoid muscle to the mandibular condyle is removed. This is likely to result in near complete loss of translatory and lateral movement of the condyle and mandible on the affected side and thus significant impairment in normal masticatory function. Elevation of both superficial and deep heads of the masseter muscle is required as well as an additional incision in the neck area in order provide access for mandibular/condyle fixation.
The overall result of current day total joint TMJ implant device procedures is a complex mechanical affair heavy in volume and weight of implant materials. Such procedures necessitate highly invasive surgical procedures with extensive resection of joint structures and multiple extensive incisions in the facial and neck region for access purposes and subsequent prolonged hospitalizations. Such procedures also carry a significant risk of infection because of the mass of implant material involved. In some case, there may also be other undesirable developments such as the formation of fibrous adhesions in and around joint structures with accompanying restriction of motion as well as excessive reactive boney exostosis.